Cardiotachometer using autocorrelation techniques

Abstract

A cardiotachometer for indicating heart rate of a user in beats per minute. The cardiotachometer comprises a sensor, placed on the body of the user, for producing an electrical signal indicative of the heart rate of the user. Circuitry is provided for converting the electrical signal into first and second digital signals. 60/t computation circuitry responds to the first and second digital signals and produces a third digital signal having a varying frequency representative of the number of heart beats per minute. An up-counter converts the third digital signal into a plurality of binary number signals, each bit of which is stored in a series of shift registers. A compare using a plurality of exclusive OR gates, compares each of the stored binary number signals with the most recent binary number signal, from the up-counter, to determine if a plurality of compared signals are within a predetermined percentage of each other. Finally, a display is provided for displaying the most recent binary number signal, when the plurality of compared signals are within the predetermined percentage of each other. Further provision is made for display of both elapsed time and time of day.

What is claimed is: 
     
       1. A cardiotachometer for indicating heart rate of a user in beats per minute, said cardiotachometer comprising: means, responsive to the heart beats of said user for producing a heart rate signal having portions representative of the beats per minute of said user's heart;   means for storing the portions of said heart rate signal;   means for comparing each of said stored portions with the most recent portion of said heart rate signal;   means for issuing a display signal when at least two of the comparisons in said comparing means is made between portions within a predetermined comparison range; and   means, responsive to said display signal, for displaying said most recent portion of said heart rate signal in eye-readable format wherein heart rate in beats per minute is indicated.   
     
     
       2. The cardiotachometer of claim 1, wherein said at least two is three. 
     
     
       3. The cardiotachometer of claim 1 further including time delay means for removing spurious pulses. 
     
     
       4. A cardiotachometer for indicating heart rate of a user in beats per minute, said cardiotachometer comprising: interval means, responsive to the heart beats of said user, for producing an interval signal having portions indicative of the time interval between said beats;   means for converting each portion of said interval signal into a heart rate signal having portions representative of the beats per minute of said user's heart;   means for storing the portions of said heart rate signal;   means for comparing each of said stored portions with the most recent portion of said heart rate signal;   means for issuing a display signal when at least two of the comparisons in said comparing means are made between portions within a predetermined percentage of each other; and   means, responsive to said display signal, for displaying said most recent one of said plurality of signals in eye-readable format wherein heart rate in beats per minute is indicated.   
     
     
       5. The cardiotachometer of claim 4, further comprising sensor means, adapted to contact the skin of said user, for producing an electrical signal indicative of the heart beats of said user, and interconnect means for conveying said electrical signal for use by said interval means. 
     
     
       6. The cardiotachometer of claim 4 further including time delay means for removing spurious pulses. 
     
     
       7. The cardiotachometer of claim 4, further comprising means for producing a signal indicative of time-of-day for display by said displaying means. 
     
     
       8. The cardiotachometer of claim 4, further comprising means for producing a signal indicative of elapsed time for display by said displaying means. 
     
     
       9. A cardiotachometer for indicating heart rate in beats per minute of a user, said cardiotachometer comprising: sensor means, adapted to contact the skin of said user, for producing an electrical signal inidicative of the heart rate of said user;   means for converting said electrical signal into first and second digital signals;   means responsive to said first and second digital signals for producing a third digital signal having a varying frequency representative of the number of heart beats per minute;   converting means for converting said third digital signal into a plurality binary number signals;   storing means for storing each of said binary number signals;   means for comparing each of said stored binary number signals with the most recent binary number signal from said converting means to determine if a plurality of compared signals are within a predetermined comparison range of each other; and   means for displaying said most recent binary number signal when said plurality of compared signals are within said predetermined percentage of each other.   
     
     
       10. The cardiotachometer of claim 9, wherein said comparison range is determined by the number of least significant bits excluded from each of said stored and most recent binary number signals. 
     
     
       11. The cardiotachometer of claim 9, wherein said sensor means comprises a pressure transducer. 
     
     
       12. The cardiotachometer of claim 9, wherein said sensor means comprises a light source, and a photocell responsive to variations in light intensity reflected off of the capillary bed within the skin of said user, for producing a voltage signal representative of the heart rate of said user. 
     
     
       13. The cardiotachometer of claim 9, wherein said sensor means detects systolic beats in order to produce said electrical signal. 
     
     
       14. The cardiotachometer of claim 9, wherein said third digital signal producing means comprises counting means for producing an interval signal representing the time interval between heart beats, and dividing means responsive to said interval signal for producing said third digital signal. 
     
     
       15. The cardiotachometer of claim 14, wherein said producing means includes a latch for holding said interval signal before it is fed to said dividing means. 
     
     
       16. The cardiotachometer of claim 15, wherein said dividing means is a divide-by-N device. 
     
     
       17. The cardiotachometer of claim 9, wherein said converting means comprises an up-counter. 
     
     
       18. The cardiotachometer of claim 9, wherein said storing means comprises shift register means. 
     
     
       19. The cardiotachometer of claim 9, wherein said plurality of binary number signals each comprises a plurality of bits, and said storing means comprises a plurality of shift registers, each for receiving a particular bit of each binary number signal. 
     
     
       20. The cardiotachometer of claim 9, wherein said comparing means includes an exclusive OR gate for receiving said stored binary number signals and said most recent binary number signal. 
     
     
       21. The cardiotachometer of claim 19, wherein said comparing means further includes means for excluding at least one of the least significant bits of each of said binary number signals from being compared. 
     
     
       22. The cardiotachometer of claim 9, wherein said comparing means includes means for issuing a compare signal each time said compared signals are within a predetermined percentage of each other, and wherein said displaying means includes means for issuing a display signal after receiving a plurality of said compare signals. 
     
     
       23. The cardiotachometer of claim 22, wherein said plurality of compare signals is three. 
     
     
       24. The cardiotachometer of claim 9, wherein said displaying means includes latch means for holding said most recent binary number signal prior to display, and means for displaying the contents of said latch means as an array of integers.